This invention relates to the establishment of telecommunications connections over packetized networks and the Public Switched Telephone Network (PSTN).
During the past few years, major improvements have been made in the transmission of voice communications over packetized networks. The simple arrangement is one wherein the voice signals are converted into Pulse Code Modulation (PCM), and these PCM signals are then sent over either an Asynchronous Transfer Mode (ATM) network basically substituting a packet network directly for the Public Switched Telephone Network (PSTN), a circuit switched network. The big progress which has been made in the use of the Internet network, a network which does not use a dedicated virtual circuit, but transmits each packet independently, has caused this network to be widely available. With the use of Internet networks, substantial delay and variations in the delay are encountered when the Internet network is relatively heavily loaded. When this happens, additional calls may be blocked and/or the quality of voice transmission may be degraded, and can become unsatisfactory. At the same time, when the Internet is not overloaded, the economics of using this type of network either already favor, or are likely in the near term future to favor, the use of the Internet network over the use of the PSTN. A problem of the prior art is how to use the combined resources of the Internet and the PSTN effectively.
Applicants have analyzed this problem further and have recognized that a problem of the prior art is that when the Internet or some equivalent packet network becomes too heavily loaded, traffic should be moved to the Public Switched Telephone Network (parts of which may use ATM transmission) for new calls and, ideally, also for calls that are already in progress. The prior art does not suggest a good arrangement for performing this type of movement, and generally leaves it up to the customer premises equipment to determine which type of network connection should be established.
The above problem is solved and an advance is made over the prior art in accordance with Applicants"" invention, wherein a local packet access network is used to access either a core packet network, such as the Internet, or the Public Switched Telephone Network (PSTN); the packet access network measures the delay of packets through the core packet network and the variation in the delay of these packets to the destination specified for a call; if this delay and/or the variation in the delay becomes excessive to the point that the quality of voice transmission becomes unsatisfactory, then new calls and existing calls are transferred to the Public Switched Telephone Network. Advantageously, the more economical network is used whenever the quality of voice transmission is satisfactory.
In accordance with one feature of Applicants"" invention, if the call is originated from an intelligent terminal, such as a personal computer (PC), then the intelligent terminal can perform measurements to determine whether the delay characteristics to the destination are satisfactory or adequate quality voice transmission, and the intelligent terminal can receive information from the packet access network to specify whether a connection should originally be established using the PSTN, because the delay and variations in delay of packets to the specified destination is excessive. Advantageously, each customer can set an individual threshold of acceptable delay and acceptable variations in delay.
In accordance with Applicants"" preferred embodiment, the packet access network comprises interface circuits for interfacing with local customer stations, a common data and access controller (COMDAC), and a packet switch. The COMDAC converts PCM signals generated by the interface circuits into packets, generally of the H.323 protocol used for transmitting voice over the Internet, for use by the packet switch and the packet switch accesses a core packet network 25, such as the Internet, directly, and accesses the PSTN 32 via a PSTN gateway and an end office switch. The common data and access controller in Applicants"" preferred embodiment, converts individual voice communications destined for the core packet network into H.323 packets, or into PCM packets for transmission to the PSTN gateway. In accordance with another feature of Applicants"" invention, the COMDAC also performs routine measurements on inter-packet delay for voice communications to different destinations, for those stations not directly connected to the packet switch.
In accordance with another feature of Applicants"" preferred embodiment, intelligent customer premises equipment communicates directly with the packet switch without passing through the COMDAC. Effectively, the PC performs many of the functions of the COMDAC.
In accordance with Applicants"" preferred embodiment, the packet switch of the access network is connected to a server system which includes a call feature server for analyzing customer dialed information and combining this data with information about the customer from a customer database in order to determine the routing of a call, routed via the core packet network. The call feature server also provides standard PSTN features (3-way calling, call forwarding, call waiting, etc.), for calls routed via the packet core network. The COMDAC communicates with the server system via the packet switch. A complex server system comprising a plurality of servers, can be used to further control a plurality of COMDAC""s. For calls routed via the PSTN, the PSTN provides feature control.
The Server system of Applicants"" preferred embodiment also includes a resource service, for providing such functions as dialed digit collection, digit out-pulsing, conference circuits, etc. The server system also includes a signaling gateway for communicating with other switches for PSTN calls when sending packet originated calls through the PSTN.